Turbocharger

ABSTRACT

A turbocharger includes an exhaust nozzle arranged between a scroll passage of a turbine housing and a turbine impeller, a gap formed between a rear surface of the exhaust nozzle and the turbine housing, and a sealing device for closing the gap. The sealing device includes a seal member which is C-shaped, i.e., an annulus with a part cut out to provide a slit, and has an inner peripheral end arranged along the turbine housing. The seal member is configured such that, by action of gas pressure in the scroll passage, the outer peripheral end approaches the rear surface of the exhaust nozzle, slit ends approach to each other, and the inner peripheral end approaches the turbine housing, leading to reduction in diameter. With a simple structure, gas is prevented from leaking from higher to lower pressure sides through a gap between a turbine housing and an exhaust nozzle.

TECHNICAL FIELD

The present invention relates to a turbocharger wherein gas is preventedfrom leaking from higher pressure side to lower pressure side through agap between a turbine housing and an exhaust nozzle.

BACKGROUND ART

FIG. 1 shows a conventional variable displacement turbocharger to whichthe invention is applied. In the turbocharger, turbine and compressorhousings 1 and 2 are integrally assembled through a bearing housing 3 byfastening bolts 3 a and 3 b, a turbine impeller 4 in the turbine housing1 being connected to a compressor impeller 5 in the compressor housing 2by a turbine shaft 7 rotatably supported via a bearing 6 in the bearinghousing 3.

As shown in FIG. 2 in enlarged scale, the bearing housing 3 is provided,on its turbine housing 1 side, with an exhaust nozzle 9 by which thefluid (exhaust gas) introduced into a scroll passage 8 in the turbinehousing 1 is guided to the turbine impeller 4.

The exhaust nozzle 9 comprises front and rear exhaust guide walls 10 and11 on sides of the bearing and turbine housings 3 and 1, respectively,integrally assembled together with a required distance being retainedbetween them by, for example, three fixing members 12 arrangedcircumferentially. Upon assembling of the turbine and bearing housings 1and 3, an attachment member 13 fixed to a front surface of the frontwall 10 (i.e., a surface adjacent to the bearing housing 3) is clampedby the housings 1 and 3 to fix the exhaust nozzle 9. Upon theassembling, the exhaust nozzle 9 is positioned relative to the bearinghousing 3 by a positioning pin 14.

Annularly arranged between the front and rear walls 10 and 11 are aplurality of nozzle vanes 15 each of which is rotatably supported atleast by a vane shaft 16 a extending through the front wall 10. In FIGS.1 and 2, each of the nozzle vanes 15 is dually supported such that thenozzle vane 15 has vane shafts 16 a and 16 b fixed to opposite sides ofthe vane 15 and extending through the front and rear walls 10 and 11,respectively. Alternatively, the nozzle vane 15 may be supported in acantilever manner only by the vane shaft 16 a extending through thefront wall 10.

In FIG. 1, reference numerals 17 a, 17 b, 17 c and 17 d designate alinked transmission mechanism for control of opening angle of the nozzlevanes 15; and 18, a scroll passage formed in the compressor housing 2.

Provided between the turbine housing 1 and the rear wall 11 of theexhaust nozzle 9 is a gap 19 which is unwanted by nature and which ishowever provided for countermeasure to, for example, possible thermaldeformation of the turbine housing 1 between during being hot and duringbeing cold and possible variations in accuracy of parts to be assembled.

The gap 19 may disadvantageously cause the exhaust gas in the passage 8to vainly leak to a turbine impeller outlet 20. Thus, in order to closethe gap 19, it has been proposed to arrange sealing piston rings 21between an outer periphery on a downstream extension 11′ of the rearwall 11 and an inner surface 1′ of the turbine housing 1 confronting theextension 11′ so as to prevent the gas leakage and absorb any thermaldeformation (see Patent Literature 1).

In Patent Literature 1, as shown in FIG. 2, formed on the outerperiphery of the extension 11′ of the rear wall 11 is an annular groove22 into which generally two sealing piston rings 21 are inserted withtheir closed gaps or cutouts being not aligned or overlapped with eachother, thereby providing a sealing device 23. The piston rings 21 arepressed at their outer peripheries against the inner surface 1′ of theturbine housing 1 by spring force of the piston rings themselves toprevent the gas leakage.

-   -   [Patent Literature 1] JP 2006-125588A

SUMMARY OF INVENTION Technical Problems

However, even with the arrangement of the piston rings 21 on the annulargroove 22 as shown in FIG. 2 for prevention of gas leakage,disadvantageously, prevention of gas leakage is still limitative. Thatis, the piston ring 21 is not an complete annulus but has a gap orcutout, so that even if the two piston rings 21 are arranged with theircutouts being not aligned, disadvantageously, gas may leak through thecutouts.

The piston rings 21, which are pressed for sealing against the innersurface 1′ of the turbine housing 1 through their predetermined springforce, must have high strength. Thus, even if the inner surface 1′ ismachined with high degree of circularity, spacing may be producedbetween the inner surface 1′ and the piston rings 21 when the pistonrings 21 have slight distortion in circularity, disadvantageouslyresulting in gas leakage through outer peripheries of the piston rings21.

The invention was made in view of the above and has its object toprovide a turbocharger which is simple in structure and which caneffectively prevent gas from leaking from higher pressure side to lowerpressure side through a gap between a turbine housing and an exhaustnozzle.

Solution to Problems

The invention is directed to a turbocharger having an exhaust nozzlebetween a scroll passage of a turbine housing and a turbine impeller, agap between a rear surface of said exhaust nozzle and said turbinehousing and a sealing device for closing said gap, characterized in thatsaid sealing device comprises a seal member in the form of an annuluswith a part cut out for provision of a slit and having an innerperipheral end arranged along said turbine housing, said seal memberbeing configured such that, by the action of gas pressure in the scrollpassage, an outer peripheral end of the member approaches the rearsurface of the exhaust nozzle, slit ends of the member approach to eachother and an inner peripheral end of the member approaches said turbinehousing, resulting in decrease in diameter of the member.

It is preferable in the turbocharger that said slit is formed to havedistance at the outer peripheral end greater than that at the innerperipheral end.

It is preferable in the turbocharger that said seal member issubstantially frustoconical to have diameter gradually increased fromturbine housing side to exhaust nozzle side.

ADVANTAGEOUS EFFECTS OF INVENTION

In the invention, an inner peripheral end of a seal member is arrangedalong a step on a turbine housing so that, by the action of gas pressurein the scroll passage, an outer peripheral end of the seal memberapproaches the rear surface of the exhaust nozzle and, due to pressuredifference between the gas pressure in the scroll passage and thepressure in the gap, the slit ends approach to each other and the innerperipheral end of the member approaches the step, leading to reductionin diameter of the seal member. As a result, the invention has anexcellent effect that, with a simple structure, a gap between theturbine housing and the rear surface of the exhaust nozzle can be closedwith high sealability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional side view of a conventional turbocharger;

FIG. 2 is a sectional side view of the nozzle and its vicinity in FIG.1;

FIG. 3 is a sectional side view of a nozzle and its vicinity showing anembodiment of the invention;

FIG. 4 is a sectional side view which is different from FIG. 3 in how tosupport the nozzle vanes of the exhaust nozzle;

FIG. 5 is a front view of the seal member shown in FIGS. 3 and 4;

FIG. 6 is a front view showing an example of slit shape in the sealmember of FIG. 5;

FIG. 7 is a sectional side view showing a nozzle and its vicinity in afurther embodiment of the invention; and

FIG. 8 is a sectional side view showing a nozzle and its vicinity in avariation of FIG. 7.

REFERENCE SIGNS LIST

-   1 turbine housing-   4 turbine impeller-   8 scroll passage-   9 exhaust nozzle-   19 gap-   25 sealing device-   28 inner peripheral end-   29 seal member-   29 a, 29 b slit end-   30 slit-   33 outer peripheral end

DESCRIPTION OF EMBODIMENTS

Embodiments of the invention will be described in conjunction with theattached drawings.

FIG. 3 is an embodiment of the invention applied to the turbochargershown in FIGS. 1 and 2 in which a sealing device 25 is arranged betweena turbine housing 1 and a rear surface 24 of an exhaust nozzle 9 so asto prevent gas in a scroll passage 8 from leaking via a gap 19 betweenthe housing 1 and the surface 24 of the nozzle 9 to the turbine impeller4.

FIG. 3 shows an application to a turbocharger with the exhaust nozzle 9where each of nozzle vanes 15 is supported at its opposite sides suchthat vane shafts 16 a and 16 b fixed to the opposite sides of the vane15 extend through front and rear exhaust guide walls 10 and 11,respectively. The sealing device 25 is similarly applicable to theturbocharger with the exhaust nozzle 9 as shown in FIG. 4 where each ofthe nozzle vanes 15 is supported in a cantilever manner such that onlythe vane shaft 16 a extends through the front exhaust guide wall 10.

In the sealing device 25, a cylindrical step 27 in parallel with theturbine shaft is formed on an outer periphery of a portion 26 of theturbine housing 1 confronting the rear surface 24 of the exhaust nozzle9 to provide the gap 19; and a seal member 29 is arranged on and fittedat its inner peripheral end 28 to the step 27.

The seal member 29 comprises, as shown in FIG. 5, a substantiallyfrustoconical metal sheet which is peripherally cut out into C-shape toprovide a slit 30 with width of the order of 0.2-0.8 mm. The innerperipheral end 28 of the seal member 29 is bent, as shown in FIGS. 3 and4, in a direction away from the exhaust nozzle 9 to be fitted to thestep 27. An outer peripheral end 33 of the seal member 29 comprises aconical straight portion 31 with diameter increased from the innerperipheral end 28 toward an outer peripheral end of the rear surface 24of the exhaust nozzle 9 and a portion 32 curved for close contact withthe rear surface 24 of the exhaust nozzle 9.

In this respect, the inner peripheral end 28 of the seal member 29 isfitted to the step 27 with slight spacing between them which allows itsaxial movement due to gas pressure in the scroll passage 8. The sealmember 29 is formed to have deformation strength in terms of thicknesswhich allows mutual approaching of the slit ends 29 a and 29 b due tothe gas pressure in the scroll passage 8 for reduction in diameter.

More specifically, the gas pressure in the scroll passage 8 acts on theseal member 29; in this time, the slit 30 in communication with the gap19 has pressure lower than the gas pressure in the scroll passage 8. Asa result, due to the pressure difference between the gas pressure actingon the seal member 29 and the pressure at the slit 30, the slit ends 29a and 29 b receive mutually attractive powers to approach to each otherand the inner peripheral end 28 also approaches the step 27, leading toreduction in diameter of the seal member 29.

In order to make the slit ends 29 a and 29 b into substantially closecontact with each other when the diameter of the seal member 29 isreduced as mentioned in the above, the slit 30 may be wedge-shaped asshown in FIG. 6 such that the distance of the same is graduallyincreased from distance S1 at the inner peripheral end 28 to distance S2at the outer peripheral end 33.

Mode of operation of the above embodiment is as follows.

In the embodiment shown in FIGS. 3 and 4, after the inner peripheral end28 of the seal member 29 shown in FIG. 5 is fitted to the step 27 formedon the turbine housing 1, the turbine housing 1 is integrally assembledto the bearing housing 3, using a fastening bolt 3 a as shown in FIG. 1.

As shown in FIG. 3 or FIG. 4, the seal member 29 arranged in the turbinehousing 1 is urged by gas pressure in the scroll passage 8 (pressuredifference between pressure in the scroll flow passage 8 and pressure inthe gap 19) in a direction of arrow A, so that the curved portion 32 ofthe outer peripheral end 33 of the seal member 29 approaches and isclosely fitted to the rear surface 24 of the rear wall 11 of the exhaustnozzle 9.

Meanwhile, since the pressure at the slit 30 (see FIG. 5) is lower thanthe gas pressure acting on the seal member 29, such pressure differencecauses the slit ends 29 a and 29 b to approach to each other and at thesame time the inner peripheral end 28 also approaches the step 27, whichreduce the diameter of the seal member 29.

Thus, the outer peripheral end 32 of the seal member 29 is closelyfitted to the rear surface 24 of the exhaust nozzle 9 so that thespacing between the same and the exhaust nozzle 9 is closed and the slitends 29 a and 29 b of the seal member 29 approach to each other and theinner peripheral end 28 approaches the step 27, leading to reduction indiameter of the seal member 29. With such simple structure, the gap 19between the turbine housing 1 and the exhaust nozzle 9 can be closedwith high sealability. When, as shown in FIG. 6, the slit 30 is formedsuch that the distance S2 at the outer peripheral end 33 is greater thanthe distance S1 at the inner peripheral end 28, then as the seal member29 is reduced in diameter, the slit ends 29 a and 29 b uniformlyapproach to each other into substantially close contact with each other,thereby further enhancing the sealability at slit 30.

FIG. 7 shows a further embodiment of the invention in which a C-shapedseal member 29 has substantially L-shaped cross-section and isconfigured such that by the action of the gas pressure in the scrollpassage 8 the outer peripheral end 33 approaches the rear surface of therear wall 11 of the exhaust nozzle 9, and as shown in FIG. 5 the slitends 29 a and 29 b approach to each other and the inner peripheral end28 approaches the step 27 formed on the turbine housing 1, leading toreduction in diameter of the member. Also with the shape of the sealmember 29 shown in FIG. 7, the exhaust gas pressure in the scrollpassage 8 is utilized to close the gap 19 so that leakage of exhaust gasthrough the gap 19 can be reduced. In the FIG. 7 embodiment, aprojection 35 extends from the turbine housing 1 to provide a guidespacing 34 at the outer periphery of the rear exhaust guide wall 11, aguide chamber 36 in communication with the guide spacing 34 being formedon the turbine housing 1 to thereby provide a step 27 on which the sealmember 29 is arranged. Thus, according to the structure shown in FIG. 7,the exhaust gas from the scroll passage 8 is stably guided to theexhaust nozzle 9 by means of the projection 35.

Alternatively, the C-shaped seal member 29 may be stepped as shown inFIG. 8 such that the inner peripheral end 28 extends along the step 27toward the exhaust nozzle 9, extends radially outwardly and then extendin parallel with the turbine shaft toward the exhaust nozzle 9 so thatthe outer peripheral end 33 approaches the rear surface of the rear wall11 of the exhaust nozzle 9; or it may be of other various shapes.

The above-mentioned seal member 29, which may be very simple instructure, can be produced at inexpensive costs and with highproductivity.

As shown in FIG. 3, the sealing device 25 with the seal member 29 isarranged for sealing upstream, in the exhaust gas flow, of athrough-hole 16′ (i.e., at the scroll passage 8 side) via which eachvane shaft 16 b extends through the rear exhaust guide wall 11 so thatdue to the fact that the pressure in the gap 19 downstream of the sealmember 29 is lower than the pressure of the exhaust gas flowing throughthe exhaust nozzle 9, the exhaust gas in the exhaust nozzle 9 flowsthrough the through-hole 16′ for the vane shaft 16 b into the gap 19;moreover, due to the pressure difference between the pressure in theexhaust nozzle 9 and the pressure in the gap 19, the nozzle vane 15 isurged and displaced to the rear exhaust guide wall 11 so that a flange16″ on the vane shaft 16 b is pushed to the rear wall 11 to close thethrough-hole 16′. As a result, the gas in the exhaust nozzle 9 isprevented from flowing through the through-hole 16′ for the vane shaft16 b into the gap 19, thereby enhancing the sealability.

It is to be understood that the present invention is not limited to theabove embodiments and that various changes and modifications may be madewithout leaving the scope of the invention.

INDUSTRIAL APPLICABILITY

With the invention, the turbocharger is provided with a seal memberwhich is utilized for enhancement of the sealability of theturbocharger, the seal member being configured such that, by the actionof the gas pressure in the scroll passage, the outer peripheral endapproaches the rear surface of the exhaust nozzle, the slit endsapproach to each other and the inner peripheral end approaches theturbine housing, leading to reduction in diameter of the member.

1. A turbocharger comprising: an exhaust nozzle between a scroll passageof a turbine housing and a turbine impeller; a gap between a rearsurface of said exhaust nozzle and said turbine housing; and a sealingdevice for closing said gap, wherein said sealing device comprises aseal member in the form of an annulus partly cut out for provision of aslit and having an inner peripheral end arranged along said turbinehousing, said seal member being configured such that, by the action ofgas pressure in the scroll passage, an outer peripheral end of themember approaches the rear surface of the exhaust nozzle, slit ends ofthe member approach to each other and an inner peripheral end of themember approaches said turbine housing, resulting in decrease indiameter of the member.
 2. A turbocharger as claimed in claim 1, whereinsaid slit is formed to have distance at the outer peripheral end greaterthan that at the inner peripheral end.
 3. A turbocharger as claimed inclaim 1, wherein said seal member is substantially frustoconical to havediameter gradually increased from turbine housing side to exhaust nozzleside.
 4. A turbocharger as claimed in claim 2, wherein said seal memberis substantially frustoconical to have diameter gradually increased fromturbine housing side to exhaust nozzle side.